In an impassioned recorded speech on the first night of the Republican National Convention, which saw her shouting by the end, Ms Guilfoyle said Joe Biden and Kamala Harris would "destroy" the country and "enslave" Americans with a "victim ideology" if elected.
Ms Guilfoyle, who serves as chair of the Trump Victory Finance Committee, was previously married to Gavin Newsom, the current Democratic governor of California, making her attack on America's most populous state all the more striking.
In her address to the RNC the 51-year-old said: "If you want to see the socialist Biden-Harris future for our country, just take a look at California.
"It is a place of immense wealth, immeasurable innovation and immaculate environment. And the Democrats turned it into a land of discarded heroin needles in parks, riots in streets and blackouts in homes."
She added: "In President Trump's America we light things up, we don't dim them down. We build things up, we don't burn them down. We kneel in prayer and we stand for our flag."
Referring to her Latina heritage, she warned that if the Democrats are elected in November, the US will follow in the socialist footsteps of Cuba and Venezuela.
She added: "President Trump believes in you. He emancipates and lifts you up to live your American Dream. You are capable, you are qualified, you are powerful, and you have the ability to choose your life, and determine your destiny.
"Don't let the Democrats take you for granted. Don't let them step on you. Don't let them destroy your families, your lives and your future. Don't let them kill future generations because they told you and brainwashed you and fed you lies that you weren't good enough."
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